1. Field of Invention
The present invention relates to electrode systems and methods for reducing motion artifact.
2. Description of Related Art
Medical practitioners use many medical field applications when diagnosing a patient. For example, the medical practitioner can use an electrocardiogram (ECG) or other monitoring, recording and analyzing systems such as electrogastrograms, electroencephalograms or electromyograms. An electrocardiogram (ECG) is a body surface manifestation of electrical potentials produced by a beating heart. The ECG is a prescribed diagnostic procedure in medicine and can be used, for example, to diagnose heart disease, identify irregular cardiac rhythms (arrhythmias), evaluate the effects of drugs, and monitor surgical procedures. The magnitude, conduction and duration of these potentials can be detected by placing an electrode on the skin of a patient.
Errors in the form of noise can occur when the ECG is performed on a patient. For example, motion artifact is noise that is introduced to the ECG signal that can result from motion of an electrode that is placed on the skin of a patient. The presence of motion artifact can result in misdiagnosis, prolong procedure duration and can lead to delayed or inappropriate treatment decisions. Thus, it is imperative to remove motion artifact from the ECG signal to prevent these problems from occurring during treatment.
Methods for reducing the effects of motion artifact in the ECG have been disclosed which focus of the skin deformation. These methods include removing the epidermal layer of the skin by abrasion, puncturing the skin in the vicinity of the electrode, and measuring skin stretch at the electrode site. The methods for skin abrasion ensure good electrical contact between the electrode and the patient's skin. In this method, an abrasive pad is mechanically rotated on the skin to abrade the skin surface before electrode placement. Moreover, medical electrodes have been used with an abrading member to prepare the skin after application of the electrode whereby an applicator gun rotates the abrading member. Methods of skin preparation that abrade the skin with a bundle of fibers have also been disclosed. The methods discussed above provide a light abrasion of the skin to reduce the electrical potential and minimize the impedance of the skin, thereby reducing motion artifacts. However, skin abrasion methods can cause unnecessary patient discomfort, prolong procedure preparation time and can vary based on operator experience. Furthermore, skin abrasions methods can lead to infection, and do not provide an effective solution to long term monitoring.
A method using an electrode that includes penetration tines to puncture the skin, and reduce skin impedance and the skin's propensity to generate motion artifact has also been disclosed. However, methods involving skin puncture can also cause the problems discussed above to occur.
A method using an electrode with a sensor incorporated in the cap to measure cable motion is also known. The cable motion is measured and is used to filter motion artifact. Electrode assemblies incorporate cable anchors to provide strain relief and decrease motion artifact caused by cable motion. Furthermore, an electrode pad inhibits cable motion. However, these devices and methods only deal with decreasing motion artifact caused by cable motion, and do not reduce or eliminate potential initiators of motion artifact caused by the electrode motion. Although some of the methods and devices disclose a sensor enclosed within the cap, the sensor is used to measure cable motion and not the electrode motion.
Devices to measure skin stretch at the electrode site, and use this information to remove motion artifact from the contaminated signal are known. A strain gauge sensor is used to measure changes in the shape of the foam pad of the ECG electrode as a measure of skin deformation and then filter this measurement. Since the sensor is attached to the foam pad of the ECG electrode, it must be disposable which increases the overall cost of the device.
An electrode assembly with a plurality of signal acquisition areas is also known whereby the plurality of signals measure the same signal and are then received by a plurality of data acquisition devices for use in comparative studies or research applications. Although the signals can be compared to each other, they are not used to decrease the noise in the signals.
A system and method for conditioning the skin by passing electrical energy through the electrodes to minimize the skin impedance has been used to reduce motion artifact. Specifically, the systems measure the changes in the impedance around the electrode site and use those measurements to reduce motion artifact. This method is used to measure the variation in the skin's impedance around the electrode site and then transfer functions to relate this measurement to the electrode signal.
As previously discussed, the systems and methods discussed above are ineffective, cause unnecessary patient discomfort, and/or are too costly to be implemented in today's health care setting. Moreover, the above systems and methods concentrate on measuring or decreasing the mechanical artifacts.
Additional methods and systems have concentrated on solving the motion artifact problem with software algorithms and filtering. For example, one system discloses a filter system for removing small amplitude, high frequency signals from an ECG signal with a low pass filter with variable cutoff frequencies which respond to detection of a QRS complex in an ECG signal. Moreover, a device and method for filtering out baseline fluctuations from an ECG by means of a high pass or band pass filter has been disclosed. Finally, an algorithm and filtering system has been disclosed which separates the ECG signal into two signals, filters one signal, and then combines the resulting signals. However, none of these systems and methods incorporate the actual known motion of the electrode, and instead rely entirely on software filtering.
Accordingly, systems and methods are needed that reduce or eliminate the problems discussed above by measuring electrode motion by using non-disposable sensors attached to a cap of an ECG lead wire and then uses this measurement to filter motion artifact.